Figure 3.

Response of (a) velocity and (b) processivity to external force for a helicase with a 1-bp step size and a 1-bp interaction range. $h=322s^{-1}$ and ΔG = 2.25 k_BT for all curves in both panels. The interaction potential U₀ decreases from the top to the bottom curve as follows: 5 k_BT (red), 3 k_BT (blue), 2 k_BT (green), 1 k_BT (pink), and 0 k_BT (orange). The bottom-most curve (orange) therefore corresponds to a passive helicase, whereas the top two (red and blue) curves correspond to optimally active helicases. The velocity curves are plots of Eq. 9, whereas the processivity curves are plots of Eq. 12. To see this figure in color, go online.